Crimson defensive back Nick Burrello is a fifth-year senior because of a concussion.

"My junior year ... I suffered a concussion the summer coming into the year," Burrello said. "I just hit my head in the corner coming into the end zone. Got up and had horrible amnesia, and my eyes were crossed."

Repeated concussions can lead to chronic traumatic encephalopathy, a progressive degenerative brain disease also called CTE. It can occur even among players who never play beyond college.

"We’ve seen the brains of 34 athletes who didn’t play beyond college, and 26 of them have tested positive for CTE," said Chris Nowinski, a former Harvard football player who now works with Boston University's Center for Chronic Traumatic Encephalopathy. "That’s very concerning."

And some of them played quite recently. "There are players who have played in the last five years that we’ve seen with CTE," Nowinski added.

That's why Nowinski is working to alert college athletes to the danger.

"We know that a ton of concussions are happening, but what’s terrible about it is that players aren’t reporting," Nowinski said. "Every game, there’s players out there playing through symptoms and lying about it."

“Every game, there’s players out there playing through symptoms and lying about it," said Chris Nowinski, a former Harvard football player who now works at BU's CTE Center and who's seen here in 2012. (David J. Phillip/AP)

A study published earlier this year concludes a quarter of college athletes experience pressure from coaches, teammates, parents and fans to continue playing while having symptoms after a suspected concussion.

"The hardest pressure to overcome is peer pressure, and the peers really care for you here," Burrello said. "There is a sense of brotherhood and camaraderie here that's formed from the top down, from Coach Murphy down. He preaches family, brotherhood, and we really take that to heart. So if you are hurting, there's players on the team that'll take you on the side, your best friends, guys who are going to be in your wedding, will be like: 'Listen, your health comes first.' "

The day after he suffered his concussion, Burrello went to see Harvard's head athletic trainer. And because his eyes were crossed, he was sent to Massachusetts General Hospital for physical therapy.

The Ivy League's 'Big Commitment'

The NCAA recommends baseline testing to all colleges and universities, and it recommends that no player be allowed to return to play until that player has returned to his or her baseline levels. Harvard does baseline testing for brain function and balance on its freshman athletes.

Some other local institutions -- like Boston College, MIT and Tufts, for instance — also follow the recommendations.

But a Harvard study last year found that nearly 1 in 5 NCAA schools either had no concussion management plan or failed to adequately educate staff about such a plan. Researchers have also completed a study examining implementation of baseline testing across NCAA member schools; it is currently under academic review.

The Ivy League, and Harvard in particular, have led the way in trying to prevent brain damage from concussions in college football.

BU's Nowinski worked with the Ivy League to implement its concussion management program.

"The Ivy League’s made a big commitment to managing concussions in a very strict way, prioritizing the player’s health, so for example, the player can’t return to the field until they can return full-speed to the classroom, and that's something that we're trying to get everybody to do," he said.

At Harvard, head injury management meant Burrello could take his time.

"I really didn't feel pressure to come back immediately and put my health at risk," Burrello said. "They really stressed that you need to take the time to have your brain come back to 100 percent. And so I did not come back until I felt I was comfortable and 100 percent to come back, and I also had to pass a physical exam, a mental exam, my impact test."

Harvard players with concussions are given academic concessions to ensure cognitive rest. That was the case with Burrello. "My professors were very helpful," he said. "They extended my deadlines."

Harvard's goal is to return players to a normal academic life first. Only then they can return to their athletic pursuits.

That's now standard practice across the Ivy League.

Sub-Concussive Hits 'The Elephant In The Room'

Linemen and linebackers are football positions most at risk for sub-concussive hits. (Jesse Costa/WBUR)

Studies show more than half the hits football players take come in practice. Harvard led the way by limiting contact practice to twice a week, and the Ivy League followed suit. The PAC 12 conference now also limits full-contact practices to two a week.

Harvard limits full-contact practice in part out of concern about sub-concussive hits. Because these blows to the head do not produce any symptoms, a concussion is not diagnosed.

Even so, Burrello is not aware of any discussion of sub-concussive injuries.

"Not that I know of, and I had a pretty bad concussion," Burrello said. "I came back. You might get hit in the head once in awhile, but it's not like: 'Oh, my gosh! I must have a concussion again.' It's not that bad, by any means. You can make full recovery and still take everything in stride."

As a safety, Burrello did not play one of the positions most at risk for sub-concussive hits. Those would be the linemen and the linebackers.

Harvard's head athletic trainer says the university discusses concussions with all its athletes every year. And Harvard athletes are taking part in a study with the medical school studying the effects of sub-concussive hits.

Sub-concussive injuries are what Robert Cantu, co-director of BU's CTE Center, says injury management practices should be focusing on.

"I see the sub-concussive issue as the elephant in the room, in the sense that it's less well understood," Cantu said in an interview. "Concussions have gotten quite a bit of recognition in recent years, maybe too much, in some ways, because it's total brain trauma that counts."

Cantu says just the accumulation of these blows can give rise to cognitive impairment. He cites more than 10 studies that have looked at sub-concussive blows alone.

But his colleague, Nowinski, says his own experience confirms studies that players still don't even consider concussions to be a serious injury. He recalls a recent address he gave at a Division III school, Texas Lutheran.

"The football team was there," Nowinski remembered, "and the next morning, the athletic trainer let me know that a player came in and said: 'I’ve had a headache for four days. I’ve been hiding it, but now that I understand the consequences, I’m here to tell you.' And it just reminds me that the players aren’t getting enough education."